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Airbox mod

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cjhukill(at)cox.net
Guest

Posted: Mon Aug 25, 2014 2:39 pm Post subject: Airbox mod

I have yet another mod that I did, this time to the fab airbox. With all the 

feedback of the problems that some have had with the various Vans versions 

of alternate air devises, I wasn't thrilled with any of them. My design 

criteria is that there should be zero chance of ingesting anything into the 

motor. That includes hardware that came loose from the fab, or anything else 

the engine could suck in while in "alternate air" mode. That would even 

include dirty, dusty or sandy air. The second feature would be that the 

bypass must occur automatically. If I suck in a bird at 200 feet agl, right 

after takeoff, I don't want to have to remember that bypass knob in the few 

seconds before crashing. The solution was to use reed valves, as others have 

done, but locate them not below the fab, but behind it. The aft section of 

the filter is isolated with small dams, and when the reed valves suck in, 

the air goes thru that section of the filter that isn't contaminated. In 

that mode you still are breathing clean air, although at a slight decrease 

in power due to loss of ram air. How much power? Tests on my flying RV8 

showed about a 10% reduction during full power static runs. I will run a 

similar test when I get the 10 flying. I have attached pictures, but they 

may not come thru. If interested email me off-forum and I'll send them.

Chris Hukill

still being baffled by baffles

fab_complete.jpg

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Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Mon Aug 25, 2014 4:54 pm Post subject: Re: Airbox mod

I'm all in favor of a better mousetrap, but a few things would bother me here.

1. I'd worry about the 'good' part of the filter getting water soaked from the inside, then later freezing.

2. At WOT you'll need something like a 200 ft/sec airflow thru those three holes, not sure if that is possible.

_________________
Bob Turner
RV-10 QB

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Mon Aug 25, 2014 5:08 pm Post subject: Airbox mod

It did occur to me that one could mount a plate in front of the air filter to fore the air to make a turn, so that any snow, sleet, ice, hail etc would impact on the plate rather than the filter. Some cars used to have an arrangement like that. 

 

I think if you are getting enough water to wet the back side of the filter you are in weather a light single has no business being there. Any time air has to change direction any liquid or solids will not make the turn. If the air is cold enough to refreeze water it means it is cold enough for ice on the airframe as well. I don't know what prompted Vans to even offer an alternate air, since they obviously believe in Day VFR as the conditions to fly an RV.

 

So far I have not  been convinced of the need for alternate air in the FAB as the plans show it. Maybe if you fly through a volcanic ash cloud you might severely plug the whole filter. And then you are faced with either loss of power or ruining the engine by opening the alt air.

 

On Mon, Aug 25, 2014 at 5:54 PM, Bob Turner <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)> wrote:

 [quote]--> RV10-List message posted by: "Bob Turner" <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)>

  

 I'm all in favor of a better mousetrap, but a few things would bother me here.

 1. I'd worry about the 'good' part of the filter getting water soaked from the inside, then later freezing.

 2. At WOT you'll need something like a 200 ft/sec airflow thru those three holes, not sure if that is possible.

 

 --------

 Bob Turner

 RV-10 QB

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=429320#429320

 

 

 

 

 

 

 

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

saylor.dave(at)gmail.com
Guest

Posted: Mon Aug 25, 2014 5:37 pm Post subject: Airbox mod

Chris,



That's some beautiful work. Â Got a couple comments:

I don't have any numbers for how much filter area you need, but knowing Vans, I kind of doubt they provided any extra. Â What I'm saying is, how do you know you have adequate filter area remaining after you dam off the alternate part?

  



Personally, I kind of think of the air filter as doing it's job over the life of the engine. Â The odds of inhaling an adequately foreign object -- while running alternate air -- seem small enough to me to tolerate the risk.

  



How do you know it's working? Â Indicator system? Â Some other parameter that changes when the alternate is open?

While you're at it, look in the archives about mounting an aluminum plate under the filter. Â It tends to wear through the bottom of the FAB.

  



Blue Skies,

--Dave





On Mon, Aug 25, 2014 at 3:38 PM, Chris Hukill <cjhukill(at)cox.net (cjhukill(at)cox.net)> wrote:

  [quote]I have yet another mod that I did, this time to the fab airbox. With all the feedback of the problems that some have had with the various Vans versions of alternate air devises, I wasn't thrilled with any of them. My design criteria is that there should be zero chance of ingesting anything into the motor. That includes hardware that came loose from the fab, or anything else the engine could suck in while in "alternate air" mode. That would even include dirty, dusty or sandy air. The second feature would be that the bypass must occur automatically. If I suck in a bird at 200 feet agl, right after takeoff, I don't want to have to remember that bypass knob in the few seconds before crashing. The solution was to use reed valves, as others have done, but locate them not below the fab, but behind it. The aft section of the filter is isolated with small dams, and when the reed valves suck in, the air goes thru that section of the filter that isn't contaminated. In that mode you still are breathing clean air, although at a slight decrease in power due to loss of ram air. How much power? Tests on my flying RV8 showed about a 10% reduction during full power static runs. I will run a similar test when I get the 10 flying. I have attached pictures, but they may not come thru. If interested email me off-forum and I'll send them.

   Chris Hukill

 still being baffled by baffles [b]

flying-nut(at)cfl.rr.com
Guest

Posted: Mon Aug 25, 2014 5:59 pm Post subject: Airbox mod

At least the alternate air wars have pushed all the other wars aside     for the time being. I don't like any control that I can't reverse.Â      That's what drove me to this:

     [img]cid:part1.00060902.09070407(at)cfl.rr.com[/img]

     

     The air hole in the bottom of the FAB is the same size as Van's     sliding one.Â  There is a piece of screen over the hole to keep out     any FOD.Â  We've seen what large birds can do .... coming through the     windshield ...... and one that nails the inlet in the cowl could     strangle your engine if you don't have alt air.Â  I have to agree     with Kelly though .... freezing rain or snow that will plug the     filter will only occur if you're flying where you shouldn't be.

     Linn

alt_air_mod_01.JPG

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Tim Olson

Joined: 25 Jan 2007
Posts: 2879

Posted: Mon Aug 25, 2014 6:21 pm Post subject: Airbox mod

You guys with the "bird through the cowl" into the intake are giving me a chuckle.  Talk about something with itty bitty small odds....  And if one DID go right into the snorkel, it would probably explode the FAB anyway, giving you a *really* large alternate air opening.



I don't know much, but other than the fact that the FAB definitely needs beefing up with a metal plate for the filter to rub on, I just don't see that much that needs more improving over a swing door in the bottom.  I don't care if I can re-set it in flight, because it'll fly fine for the remainder of that flight anyway, and I can do it on the ground. Opening it means you had an emergency.  I'm happy to take 20 minutes or whatever out of my day after a true emergency.  And in 1000+ hours I haven't had the slightest interest in pulling the knob in the first place.  All of this should be a real rare occurrence....not something like pulling carb heat on a carbureted engine...



Tim



 	  Quote: 	
		   On Aug 25, 2014, at 8:58 PM, Linn Walters <flying-nut(at)cfl.rr.com> wrote:

 

 At least the alternate air wars have pushed all the other wars aside for the time being. I don't like any control that I can't reverse.  That's what drove me to this:

 <alt air mod 01.JPG>

 

 The air hole in the bottom of the FAB is the same size as Van's sliding one.  There is a piece of screen over the hole to keep out any FOD.  We've seen what large birds can do .... coming through the windshield ...... and one that nails the inlet in the cowl could strangle your engine if you don't have alt air.  I have to agree with Kelly though .... freezing rain or snow that will plug the filter will only occur if you're flying where you shouldn't be.

 Linn

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Tue Aug 26, 2014 4:21 am Post subject: Re: Airbox mod

Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.

_________________
Wayne G.

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Tue Aug 26, 2014 5:29 am Post subject: Airbox mod

I'm curious how you reach that conclusion. There are exactly two 

limiting orifices to the engine. One is the size of the cowling openning 

to the FAB, and the other is the fuel injection servo itself. If the alt 

air openning equals the size of the cowling opening you don't have any 

restriction. If it equals the servo opening the only loss of power would 

be from the differing flow directions and loss of ram air. The surface 

area of the filter is several multiples of either of the limiting 

openings. I doubt there is very much difference in flow through the 

factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive 

and maintain(back when leaded 98 octane was available at most street 

corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at 

270 rpm will. Meaningful flow restriction by an opening only occurs when 

the pressure drop is sufficient to reach transonic speeds.

Also, look at the filter size on many certified planes in the same power 

range and I think you will find a number that are smaller than the Vans 

supplied filter. I know the filter for my 200 hp Mooney is a whole lot 

less, and the filter bypass ram air opening is about the same size as 

the flange to the fuel servo.

On 8/26/2014 5:21 AM, rv10flyer wrote:

 	  Quote: 	
		   



 Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.



 --------

 Wayne G.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=429341#429341

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

carl.froehlich(at)verizon
Guest

Posted: Tue Aug 26, 2014 6:25 am Post subject: Airbox mod

If you invert the top cover of the stock Van's air box it will now fit the

taller K&N E-1000 filter. 



As previously stated, recommend adding an aluminum plate between the bottom

of the filter and the fiberglass air box bottom.  From experience I know the

filter will ablate the fiberglass over time.  Talking to Van's on this they

are now recommending the same for people who call them about the problem.

Hopefully they will update the plans to reflect.



Carl

--

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Tue Aug 26, 2014 6:58 am Post subject: Re: Airbox mod

From K & N website...



A = (C.I.D. x RPM) / 20,839



A= 540 X 2,700 / 20,839



A= 70 sq in. 



I already measured mine and it is undersized. One of the reasons many complain of "shrinking filters". Pressure differential, fuel, oil, rain, high heat also contribute. 



Measure your RV-10 filter ensuring you subtract the 3/4" rubber seals and see what you come up with. 



 	  Kellym wrote: 	
		  I'm curious how you reach that conclusion. There are exactly two 

limiting orifices to the engine. One is the size of the cowling openning 

to the FAB, and the other is the fuel injection servo itself. If the alt 

air openning equals the size of the cowling opening you don't have any 

restriction. If it equals the servo opening the only loss of power would 

be from the differing flow directions and loss of ram air. The surface 

area of the filter is several multiples of either of the limiting 

openings. I doubt there is very much difference in flow through the 

factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive 

and maintain(back when leaded 98 octane was available at most street 

corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at 

270 rpm will. Meaningful flow restriction by an opening only occurs when 

the pressure drop is sufficient to reach transonic speeds.

Also, look at the filter size on many certified planes in the same power 

range and I think you will find a number that are smaller than the Vans 

supplied filter. I know the filter for my 200 hp Mooney is a whole lot 

less, and the filter bypass ram air opening is about the same size as 

the flange to the fuel servo.

On 8/26/2014 5:21 AM, rv10flyer wrote:

 	  Quote: 	
		   



 Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.



 --------

 Wayne G.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=429341#429341

_________________
Wayne G.

flying-nut(at)cfl.rr.com
Guest

Posted: Tue Aug 26, 2014 7:55 am Post subject: Airbox mod

Wayne,

Undersized? I don't think so, but I didn't take the time to measure 

mine.  It's still a virgin! Cut your old one apart and spread out the 

pleats to really measure the surface area.

So, how did you measure yours and what did you come up with?



I really believe the shrinking filter is the rubber ring reacting to 

100LL.  How many have the drain hole?  My drain hole drops down into my 

alt air mod keeping the filter rubber relatively dry.

Linn



On 8/26/2014 10:58 AM, rv10flyer wrote:

 	  Quote: 	
		   



 >From K & N website...



 A = (C.I.D. x RPM) / 20,839



 A= 540 X 2,700 / 20,839



 A= 70 sq in.



 I already measured mine and it is undersized. One of the reasons many complain of "shrinking filters". Pressure differential, fuel, oil, rain, high heat also contribute.



 Measure your RV-10 filter ensuring you subtract the 3/4" rubber seals and see what you come up with.

 Kellym wrote:

> I'm curious how you reach that conclusion. There are exactly two

> limiting orifices to the engine. One is the size of the cowling openning

> to the FAB, and the other is the fuel injection servo itself. If the alt

> air openning equals the size of the cowling opening you don't have any

> restriction. If it equals the servo opening the only loss of power would

> be from the differing flow directions and loss of ram air. The surface

> area of the filter is several multiples of either of the limiting

> openings. I doubt there is very much difference in flow through the

> factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive

> and maintain(back when leaded 98 octane was available at most street

> corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at

> 270 rpm will. Meaningful flow restriction by an opening only occurs when

> the pressure drop is sufficient to reach transonic speeds.

> Also, look at the filter size on many certified planes in the same power

> range and I think you will find a number that are smaller than the Vans

> supplied filter. I know the filter for my 200 hp Mooney is a whole lot

> less, and the filter bypass ram air opening is about the same size as

> the flange to the fuel servo.

> On 8/26/2014 5:21 AM, rv10flyer wrote:

>

>>   

>>

>>   Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.

>>

>>   --------

>>   Wayne G.

>>

>>

>>

>>

>>   Read this topic online here:

>>

>>   http://forums.matronics.com/viewtopic.php?p=429341#429341

>>

>>

>>

>>

>>

>>

>>

>>

>>

>>

>>

>>



 --------

 Wayne G.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=429357#429357





 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Tue Aug 26, 2014 9:31 am Post subject: Airbox mod

For that formula to be meaningful it has to be tied to horsepower and a few other things. It has to account for pleats in the filter as being part of the surface area. It really is a formula for the area of the filter media, not the size of the opening.

 IIRC the opening in the cowling is only about 2.25 by maybe 3.5, if that. That calculates to less than 10 sq in, more like 8. So having 70 sq in of filter area is meaningless for this discussion since the alt air usually is designed to bypass the filter. An Alt air opening that equals the inlet from the cowling is more than enough. 3X3 or equivalent. is going to provide enough air. (unless you use the wrong primer on it)

On Tue, Aug 26, 2014 at 7:58 AM, rv10flyer <wayne.gillispie(at)gmail.com (wayne.gillispie(at)gmail.com)> wrote:

 [quote]--> RV10-List message posted by: "rv10flyer" <wayne.gillispie(at)gmail.com (wayne.gillispie(at)gmail.com)>

 >From K & N website...

 A = (C.I.D. x RPM) / 20,839

 A= 540 X 2,700 / 20,839

 A= 70 sq in.

 I already measured mine and it is undersized. One of the reasons many complain of "shrinking filters". Pressure differential, fuel, oil, rain, high heat also contribute.

 Measure your RV-10 filter ensuring you subtract the 3/4" rubber seals and see what you come up with.

 Kellym wrote:

 > I'm curious how you reach that conclusion. There are exactly two

 > limiting orifices to the engine. One is the size of the cowling openning

 > to the FAB, and the other is the fuel injection servo itself. If the alt

 > air openning equals the size of the cowling opening you don't have any

 > restriction. If it equals the servo opening the only loss of power would

 > be from the differing flow directions and loss of ram air. The surface

 > area of the filter is several multiples of either of the limiting

 > openings. I doubt there is very much difference in flow through the

 > factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive

 > and maintain(back when leaded 98 octane was available at most street

 > corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at

 > 270 rpm will. Meaningful flow restriction by an opening only occurs when

 > the pressure drop is sufficient to reach transonic speeds.

 > Also, look at the filter size on many certified planes in the same power

 > range and I think you will find a number that are smaller than the Vans

 > supplied filter. I know the filter for my 200 hp Mooney is a whole lot

 > less, and the filter bypass ram air opening is about the same size as

 > the flange to the fuel servo.

 > On 8/26/2014 5:21 AM, rv10flyer wrote:

 >

 > >

 > >

 > >  Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.

 > >

 > >  --------

 > >  Wayne G.

 > >

 > >

 > >

 > >

 > >  Read this topic online here:

 > >

 > >  http://forums.matronics.com/viewtopic.php?p=429341#429341

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 >

 --------

 Wayne G.

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=429357#429357

 ===========

  target="_blank">http://www.matronics.com/Navigator?RV10-List

 ===========

 ">http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 [b]

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Tue Aug 26, 2014 9:22 pm Post subject: Re: Airbox mod

It has nothing to do with HP. It is all about moving a volume of air in a certain amount of time through the air filter. Our 540 cubic-inch engine operating at 2700 RPM flows about 380 CFM at 90% volumetric efficiency. 

From K&N website..."Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting .75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area."

No, you don't stretch the pleats out before measuring. I said nothing about his inlet or alternate air opening area. I am seeing about 30% of his EFA(Effective Filtering Area) blocked off. This from an already marginally sized filter.

[quote="Kelly McMullen"]For that formula to be meaningful it has to be tied to horsepower and a few other things. It has to account for pleats in the filter as being part of the surface area. It really is a formula for the area of the filter media, not the size of the opening.

 IIRC the opening in the cowling is only about 2.25 by maybe 3.5, if that. That calculates to less than 10 sq in, more like 8. So having 70 sq in of filter area is meaningless for this discussion since the alt air usually is designed to bypass the filter. An Alt air opening that equals the inlet from the cowling is more than enough. 3X3 or equivalent. is going to provide enough air. (unless you use the wrong primer on it)

On Tue, Aug 26, 2014 at 7:58 AM, rv10flyer <wayne> wrote:

  	  Quote: 	
		  --> RV10-List message posted by: "rv10flyer" <wayne>

 >From K & N website...

 A = (C.I.D. x RPM) / 20,839

 A= 540 X 2,700 / 20,839

 A= 70 sq in.

 I already measured mine and it is undersized. One of the reasons many complain of "shrinking filters". Pressure differential, fuel, oil, rain, high heat also contribute.

 Measure your RV-10 filter ensuring you subtract the 3/4" rubber seals and see what you come up with.

 Kellym wrote:

 > I'm curious how you reach that conclusion. There are exactly two

 > limiting orifices to the engine. One is the size of the cowling openning

 > to the FAB, and the other is the fuel injection servo itself. If the alt

 > air openning equals the size of the cowling opening you don't have any

 > restriction. If it equals the servo opening the only loss of power would

 > be from the differing flow directions and loss of ram air. The surface

 > area of the filter is several multiples of either of the limiting

 > openings. I doubt there is very much difference in flow through the

 > factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive

 > and maintain(back when leaded 98 octane was available at most street

 > corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at

 > 270 rpm will. Meaningful flow restriction by an opening only occurs when

 > the pressure drop is sufficient to reach transonic speeds.

 > Also, look at the filter size on many certified planes in the same power

 > range and I think you will find a number that are smaller than the Vans

 > supplied filter. I know the filter for my 200 hp Mooney is a whole lot

 > less, and the filter bypass ram air opening is about the same size as

 > the flange to the fuel servo.

 > On 8/26/2014 5:21 AM, rv10flyer wrote:

 >

 > >

 > >

 > >ï¿½ Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.

 > >

 > >ï¿½ --------

 > >ï¿½ Wayne G.

 > >

 > >

 > >

 > >

 > >ï¿½ Read this topic online here:

 > >

 > >ï¿½ http://forums.matronics.com/viewtopic.php?p=429341#429341

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 > >

 >

 --------

 Wayne G.

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=429357#429357

 ===========

  target="_blank">http://www.matronics.com/Navigator?RV10-List

 ===========

 ">http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 [b]

_________________
Wayne G.

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Tue Aug 26, 2014 9:35 pm Post subject: Airbox mod

You also are confusing the engine's air needs. Horsepower has everything 

to do with how much air   moves through the engine. Displacement is only 

one factor. Air is compressible, it is not a liquid, so the amount going 

through the engine and out the exhaust is much more closely related to 

power produced than it is to displacement.

Filter area needs have more to do with removal of dirt. It is irrelevant 

with any alternate air that bypasses the filter.

You only need to consider the size of the cowl opening to know the 

maximum size needed to develop rated horsepower.

With alternate air, you don't expect to get full power, but something 

more like 89 percent power, just as with a carburetor you don't get full 

power with carb heat.

On 8/26/2014 10:22 PM, rv10flyer wrote:

 	  Quote: 	
		   



 It has nothing to do with HP. It is all about moving a volume of air in a certain amount of time through the air filter. Our 540 cubic-inch engine operating at 2700 RPM flows about 380 CFM at 90% volumetric efficiency.

 >From K&N website..."Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting .75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area."



 No, you don't stretch the pleats out before measuring. I said nothing about his inlet or alternate air opening area. I am seeing about 30% of his EFA(Effective Filtering Area) blocked off. This from an already marginally sized filter.



 [quote="Kelly McMullen"]For that formula to be meaningful it has to be tied to horsepower and a few other things. It has to account for pleats in the filter as being part of the surface area. It really is a formula for the area of the filter media, not the size of the opening.

   IIRC the opening in the cowling is only about 2.25 by maybe 3.5, if that. That calculates to less than 10 sq in, more like 8. So having 70 sq in of filter area is meaningless for this discussion since the alt air usually is designed to bypass the filter. An Alt air opening that equals the inlet from the cowling is more than enough. 3X3 or equivalent. is going to provide enough air. (unless you use the wrong primer on it)

   



 On Tue, Aug 26, 2014 at 7:58 AM, rv10flyer  wrote:

   

> 

>    

>   >From K & N website...

>   

>   A = (C.I.D. x RPM) / 20,839

>   

>   A= 540 X 2,700 / 20,839

>   

>   A= 70 sq in.

>   

>   I already measured mine and it is undersized. One of the reasons many complain of "shrinking filters". Pressure differential, fuel, oil, rain, high heat also contribute.

>   

>   Measure your RV-10 filter ensuring you subtract the 3/4" rubber seals and see what you come up with.

>   

>   

>   Kellym wrote:

>   > I'm curious how you reach that conclusion. There are exactly two

>   > limiting orifices to the engine. One is the size of the cowling openning

>   > to the FAB, and the other is the fuel injection servo itself. If the alt

>   > air openning equals the size of the cowling opening you don't have any

>   > restriction. If it equals the servo opening the only loss of power would

>   > be from the differing flow directions and loss of ram air. The surface

>   > area of the filter is several multiples of either of the limiting

>   > openings. I doubt there is very much difference in flow through the

>   > factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive

>   > and maintain(back when leaded 98 octane was available at most street

>   > corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at

>   > 270 rpm will. Meaningful flow restriction by an opening only occurs when

>   > the pressure drop is sufficient to reach transonic speeds.

>   > Also, look at the filter size on many certified planes in the same power

>   > range and I think you will find a number that are smaller than the Vans

>   > supplied filter. I know the filter for my 200 hp Mooney is a whole lot

>   > less, and the filter bypass ram air opening is about the same size as

>   > the flange to the fuel servo.

>   > On 8/26/2014 5:21 AM, rv10flyer wrote:

>   >

>   > >

>   > >

>   > >ï¿½ Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.

>   > >

>   > >ï¿½ --------

>   > >ï¿½ Wayne G.

>   > >

>   > >

>   > >

>   > >

>   > >ï¿½ Read this topic online here:

>   > >

>   > >ï¿½ http://forums.matronics.com/viewtopic.php?p=429341#429341 (http://forums.matronics.com/viewtopic.php?p=429341#429341)

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   >

>   

>   

>   --------

>   Wayne G.

>   

>   

>   

>   

>   Read this topic online here:

>   

>   http://forums.matronics.com/viewtopic.php?p=429357#429357 (http://forums.matronics.com/viewtopic.php?p=429357#429357)

>   

>   

>   

>   

>   

>   

>   

>   ===========

>    target="_blank">http://www.matronics.com/Navigator?RV10-List

>   ===========

>   ">http://forums.matronics.com

>   ===========

>   le, List Admin.

>   ="_blank">http://www.matronics.com/contribution

>   ===========

>   

>   

>   

>   [b]



 --------

 Wayne G.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=429427#429427

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Tue Aug 26, 2014 10:15 pm Post subject: Re: Airbox mod

The simple formula that K&N provides gives us a MINIMUM filter area for our simple engine. Our filter is undersized according to their formula. Undersized filters equal higher air velocities, greater pressure drop and less efficient filtering. I am not an engineer and it is his airplane. 



[quote="Kellym"]You also are confusing the engine's air needs. Horsepower has everything 

to do with how much air   moves through the engine. Displacement is only 

one factor. Air is compressible, it is not a liquid, so the amount going 

through the engine and out the exhaust is much more closely related to 

power produced than it is to displacement.

Filter area needs have more to do with removal of dirt. It is irrelevant 

with any alternate air that bypasses the filter.

You only need to consider the size of the cowl opening to know the 

maximum size needed to develop rated horsepower.

With alternate air, you don't expect to get full power, but something 

more like 89 percent power, just as with a carburetor you don't get full 

power with carb heat.

On 8/26/2014 10:22 PM, rv10flyer wrote:

 	  Quote: 	
		   



 It has nothing to do with HP. It is all about moving a volume of air in a certain amount of time through the air filter. Our 540 cubic-inch engine operating at 2700 RPM flows about 380 CFM at 90% volumetric efficiency.

 >From K&N website..."Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting .75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area."



 No, you don't stretch the pleats out before measuring. I said nothing about his inlet or alternate air opening area. I am seeing about 30% of his EFA(Effective Filtering Area) blocked off. This from an already marginally sized filter.



  	  Kelly McMullen wrote: 	
		  For that formula to be meaningful it has to be tied to horsepower and a few other things. It has to account for pleats in the filter as being part of the surface area. It really is a formula for the area of the filter media, not the size of the opening.

   IIRC the opening in the cowling is only about 2.25 by maybe 3.5, if that. That calculates to less than 10 sq in, more like 8. So having 70 sq in of filter area is meaningless for this discussion since the alt air usually is designed to bypass the filter. An Alt air opening that equals the inlet from the cowling is more than enough. 3X3 or equivalent. is going to provide enough air. (unless you use the wrong primer on it)

   



 On Tue, Aug 26, 2014 at 7:58 AM, rv10flyer  wrote:

   

> 

>    

>   >From K & N website...

>   

>   A = (C.I.D. x RPM) / 20,839

>   

>   A= 540 X 2,700 / 20,839

>   

>   A= 70 sq in.

>   

>   I already measured mine and it is undersized. One of the reasons many complain of "shrinking filters". Pressure differential, fuel, oil, rain, high heat also contribute.

>   

>   Measure your RV-10 filter ensuring you subtract the 3/4" rubber seals and see what you come up with.

>   

>   

>   Kellym wrote:

>   > I'm curious how you reach that conclusion. There are exactly two

>   > limiting orifices to the engine. One is the size of the cowling openning

>   > to the FAB, and the other is the fuel injection servo itself. If the alt

>   > air openning equals the size of the cowling opening you don't have any

>   > restriction. If it equals the servo opening the only loss of power would

>   > be from the differing flow directions and loss of ram air. The surface

>   > area of the filter is several multiples of either of the limiting

>   > openings. I doubt there is very much difference in flow through the

>   > factory filter and the one I had on a 370 hp Camaro Z-28 I used to drive

>   > and maintain(back when leaded 98 octane was available at most street

>   > corners) which at 7000 rpm flowed a heck of a lot more air than a 540 at

>   > 270 rpm will. Meaningful flow restriction by an opening only occurs when

>   > the pressure drop is sufficient to reach transonic speeds.

>   > Also, look at the filter size on many certified planes in the same power

>   > range and I think you will find a number that are smaller than the Vans

>   > supplied filter. I know the filter for my 200 hp Mooney is a whole lot

>   > less, and the filter bypass ram air opening is about the same size as

>   > the flange to the fuel servo.

>   > On 8/26/2014 5:21 AM, rv10flyer wrote:

>   >

>   > >

>   > >

>   > >ï¿½ Our factory provided air filter has barely enough surface area for a 540. I would not want to remove 30% of its area for normal operations. Good luck with your mod.

>   > >

>   > >ï¿½ --------

>   > >ï¿½ Wayne G.

>   > >

>   > >

>   > >

>   > >

>   > >ï¿½ Read this topic online here:

>   > >

>   > >ï¿½ http://forums.matronics.com/viewtopic.php?p=429341#429341 (http://forums.matronics.com/viewtopic.php?p=429341#429341)

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   > >

>   >

>   

>   

>   --------

>   Wayne G.

>   

>   

>   

>   

>   Read this topic online here:

>   

>   http://forums.matronics.com/viewtopic.php?p=429357#429357 (http://forums.matronics.com/viewtopic.php?p=429357#429357)

>   

>   

>   

>   

>   

>   

>   

>   ===========

>    target="_blank">http://www.matronics.com/Navigator?RV10-List

>   ===========

>   ">http://forums.matronics.com

>   ===========

>   le, List Admin.

>   ="_blank">http://www.matronics.com/contribution

>   ===========

>   

>   

>   

>   [b]



 --------

 Wayne G.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=429427#429427

_________________
Wayne G.

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Tue Aug 26, 2014 10:40 pm Post subject: Re: Airbox mod

So let's all agree that knowing the exact answer is hard; getting an approximate answer can be had in various ways.

For a slow turning engine it's just displacement times RPM.

For a real engine, the efficiency of the intake valves can be a 10 - 20% factor, so maybe we should use power. But timing and compression ratios can affect power without changing the air flow, so that's not perfect either.

But either method should get you close.

_________________
Bob Turner
RV-10 QB

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